Data communications involve the transmission and reception of voice, data packets, and other types of information via wireless, cellular and/or mobile techniques. Hereinafter, such techniques will be simply referred to as “mobile communications” merely for the sake of brevity.
Mobile communications involve, among various processing procedures, signal transmissions and handling of data traffic between an access network (AN) and an access terminal (AT). An access network (AN) comprises many elements, one of which being a base station, as known by those skilled in the art. An access terminal (AT) can be in many forms, including a mobile station (e.g., a mobile phone), a mobile terminal (e.g., a laptop computer), and other devices (e.g., a personal digital assistant: PDA) having the combined functionality of both a mobile station and a mobile terminal, or having other terminal capabilities. Hereinafter, an access terminal (AT) will be referred to as a “mobile” for the sake of brevity.
In a typical mobile communications system, a plurality of mobile stations (e.g., cellular/mobile phones, laptop computers, personal digital assistants (PDAs), etc.) are served by a network of base stations, which allow the mobile stations to communicate with other components in the communications system. Various types of mobile communications systems and standards are known, including cellular systems, Code Division Multiple Access (CDMA), Time Division Multiple Access (TDMA), Frequency Division Multiple Access (FDMA), Personal Communication Services (PCS), and various enhancements and improvements thereto which are generally referred to as next generation mobile communications systems (including Third Generation (3G), such as IMT-2000 (International Mobile Telecommunication 2000), and Fourth Generation (4G) mobile communications systems).
CDMA is most widely accepted and continues to develop and evolve. In particular, CDMA technology evolution (such as the so-called “cdma2000” technology or other next generation CDMA systems) will provide integrated voice with simultaneous high-speed packet data, video and video conferencing capabilities. For example, systems that are evolving from CDMA include High Data Rate (HDR) technologies, cdma2000 1×EV-DV (1×EVolution—Data and Voice) and 1×Evolution—Data Only (1×EV-DO) technologies and the like.
The present disclosure focuses on data transmission techniques between base stations and mobiles. Thus, a detailed description of additional components, elements and processing procedures (not specifically mentioned herein) have been omitted so that the features of the present invention are not obscured. One skilled in the art would have understood that various other components and techniques associated with base stations and mobiles already known in the art but not described in detail herein, are also part of the present invention. For example, specific details of the protocol architecture having an air interface with a layered structure, physical layer channels, protocol negotiation and processing, and the like have been omitted.
In a communications system, a set of “channels” allow signals to be transmitted between the access network (e.g., a base station) and the access terminal (e.g., a mobile) within a given frequency assignment. Channels consist of “forward channels” and “reverse channels.” Signal transmissions (data transmissions or transfers) from the base station to a mobile via a downlink (i.e., forward channels) are commonly referred to as the “forward link,” while signal transmissions from the mobile to the base station via an uplink (i.e., reverse channels) are commonly referred to as the “reverse link.”
Typically, the forward link can comprise of a pilot channel (“pilot”), a synchronization signal channel (“sync”), a paging channel (“paging”), and a traffic channel (“traffic”). Here, a pilot signal on the pilot channel always has a constant transmission strength.
In mobile communications, the conditions of the wireless channels used All for data transmission (forward link and reverse link) often change due to the user's physical location and various mobility characteristics. There are several methods of achieving efficient use of wireless channels while allowing high-speed data transmission in a mobile communications environment. For adaptively accommodating communications environment changes in the channels, a method of changing the channel coding and a method of changing the modulation mode are known.
By using channel coding, information data is repeatedly coded to reduce error rates, and thus the amount of data transmitted on the wireless channel is increased by the repeated (redundant) data. Due to changes in the user's location and mobility, the mobile communications environment may be considered to be good or bad. When the mobile communications environment is good, coding with a high code rate having little redundancy is used to send a large amount of actual information data to increase transmission data speed. Also, when the mobile communications environment is bad, coding with a low code rate having high redundancy (being resistant to errors) is employed to allow a lower transmission data speed is used so that the transmission is resistant to noise.
For changing the modulation mode, when the mobile communications environment is good, a transmission method allowing high-speed data transmission, such as QAM (Quadrature Amplitude Modulation) or MPSK (Mary Phase Shift Keying) wherein a plurality of data bits for one transmission symbol are sent, is used. When the mobile communications environment is bad, a slow transmission method, such as BPSK (Binary Phase Shift Keying) is used despite its high level of interference noise.
Regarding the channel coding and/or the modulation mode, information that is fed back from the receiving end (e.g., the mobile in the forward link or the base station in the reverse link) is required to estimate the channel environment to be used in modifying the modulation mode and/or the channel coding.
For the reverse link, an open loop power control method is used during access procedures by the mobile. Typically, an open loop power control method refers to controlling the mobile transmit power when signals are transmitted from the mobile to the base station (i.e., on the reverse link). Namely, the transmit power of the mobile located relatively near a base station (or otherwise has a sufficient signal link with a base station) is made relatively low, while the transmit power of a mobile located relatively far from a base station (or otherwise has an insufficient signal link with a base station) is made relatively high. In this manner, the signals received by the base station from a mobile can be held relatively constant.
The open loop power control is related to the equation: Tx=constant−Rx, whereby, Tx is the transmission power strength of the mobile, and Rx is the power received from the base station (i.e., the pilot signal strength). Here, a relatively large Rx value indicates that the channel conditions are good (e.g., when the mobile is near the base station), and the Tx value is accordingly relatively small. Conversely, a relatively small Rx value indicates that the channel conditions are bad (e.g., when the mobile is far from the base station), and the Tx value is accordingly relatively large.